The hypothesis was tested that slow grain drying stimulates pre-maturity alpha-amylase activity in wheat (Triticum aestivum L.). Grain drying rate in 91 commercial crops of cultivars Avalon or Mercia grown over the years 1988–90 was estimated from the slope of linear regressions of moisture content on time. Incipient sprouting was detected in some samples from 1988 using the fluoroscein dibutyrate test, but results from a beta-limit dextrin gel assay indicated that pre-maturity alpha-amylase was probably the major source of alpha-amylase activity in these samples. Although year-to-year differences in ln alpha-amylase activity and Hagberg falling number tended to be associated with seasonal differences in drying rate, there was no evidence of a relationship between either ln alpha-amylase activity or Hagberg falling number and drying rate after the year effect was removed by an analysis of covariance. A second dataset from one crop in each of 14 years at one site showed significant positive linear relationships between cumulative potential evapotranspiration calculated over different periods during grain ripening and Hagberg falling number (excluding 3 years when incipient sprouting was thought to occur). It was concluded that pre-maturity alpha-amylase activity was stimulated by an unknown environmental factor differing between seasons and associated with seasonal differences in drying rate and cumulative potential evapotranspiration.

Year × variety means of wheat grain crude protein content (CP) and Hagberg falling number (HFN) surveyed in the UK from 1974 to 1993 were investigated with a residual maximum likelihood (REML) analysis using variety, nitrogen fertilizer application (kg N/ha), average monthly temperatures (°C), and total monthly rainfall (mm) as fixed terms, and year as a random term. Annual variety means were weighted according to the inverse of their variances. The statistical significance of fixed terms as they were added to the model was evaluated by comparing the Wald test statistic with critical values of chi-squared. CP, except for 1976 which was associated with prolonged drought conditions, was best described with a model combining effects for variety (P < 0·001), nitrogen application rate (0·0143, S.E. = 0·00312, P < 0·001), July temperature (0·184, S.E. = 0·0582, P < 0·01) and May rainfall (−0·00952, S.E. = 0·00233, P < 0·001). A model describing HFN combined effects for variety (P < 0·001), August rainfall (−0·930, S.E. = 0·2579, P < 0·001) and June temperature (24·4, S.E. = 7·37, P < 0·001). These models were evaluated for describing CP and HFN of cv. Avalon grown on sandy-loam from 1982 to 1992 at one site. Correlation coefficients of 0·51 (P = 0·1) and 0·72 (P = 0·012) were obtained between observed values at this site and those predicted from the nationally derived models for CP and HFN respectively. Variety effects suggested that the varieties commonly used in the mid 1970s would give higher CP and lower HFN than their more modern counterparts if grown at similar levels of nitrogen and in the same climatic conditions.

The effect of nitrogen and a plant growth regulator regime (chlormequat chloride followed by 2-chloroethylphosphonic acid) on the crop performance of a hybrid (cv. Luchs) and a conventionally bred winter rye (cv. Sentinel) were investigated in two field experiments each year between 1993 and 1995 at Winchester, UK. Internode length and dry weight/unit length of internodes was measured in order to assess the effect of the growth regulator regime on stem structure. Grain yields were 15% higher in the hybrid Luchs than in Sentinel. With high levels of applied nitrogen, both cultivars lodged in all seasons and this was most severe in 1994 when 88% of the crop lodged in Sentinel and 52% in Luchs. Plant growth regulator treatment consistently reduced lodging but did not eliminate it. Reductions in lodging were not always associated with an increase in grain yield. In the hybrid cultivar, the growth regulator treatment reduced yield in 1993 and 1995 when 2-chloroethyl-phosphonic acid was applied at GS49 and GS39 respectively, but increased yield in 1994 when applied at GS37. Growth regulator consistently reduced stem length, and the percentage reduction in length of the individual internodes within the stem was strongly influenced by the timing of the 2-chloroethylphosphonic acid component of the PGR treatment. Growth regulator reduced internode lengths by up to 25% in Sentinel and 35% in Luchs, and this was associated with reductions in the dry weight of internodes by up to 32% in Sentinel and 38% in Luchs. Consequently, dry weight/unit length of the stem was not increased by growth regulator treatment. Yield reductions in Luchs following growth regulator treatment may have been due to reduced stem reserves which have been associated with tolerance of stress in rye. Both cultivars were highly responsive to nitrogen. Economic optima varied from season to season, but they ranged over three years, from 175–273 kg/ha nitrogen, and were greater than the currently recommended application rates. Crop lodging increased with increasing nitrogen rate even when plant growth regulator was applied and yield penalties from lodging would have been high, if weather conditions during grain maturity had been unfavourable.

Levels of ribulose bisphosphate carboxylase (Rubisco) and Rubisco activase were compared in leaves above the ear in two genetically related populations (Z0 and Z20) of maize (Zea mays L.). Z20 was obtained from Z0 after twenty agronomic selection cycles for grain yield improvement (c. 90% above Z0). Plants were cultivated in the highlands of Mexico and leaves were sampled weekly during the grain-filling period. Chlorophyll, soluble protein and Rubisco activity were measured. Chlorophyll and soluble protein content slowly decreased during this period, the former faster than the latter, with no significant differences between populations. During the first 40 days after anthesis, Rubisco activity was significantly greater in the high-yielding population (Z20), although Western blot analysis of Rubisco showed similar values for both populations within this period. However, the same analysis for Rubisco activase indicated a greater amount of this protein in the higher-yielding population (Z20) than the original one (Z0) during the early and middle part of the grain-filling period. The addition of Rubisco activase and an ATP-generating system to Z0 leaf extracts resulted in increased Rubisco activity. It was concluded that during grain-fill in maize, the level of Rubisco activase has a regulatory effect on Rubisco activity expression.

Although there has been some recent interest in the morphology of individual white clover plants within established mixed swards under sheep grazing, there is little information available on the morphological changes taking place during the critical first 3 years of sward development. Undamaged white clover plants were sampled from an experiment at Plas Gogerddan, Ceredigion, comparing three contrasting white clover cultivars, sown with a common companion ryegrass cultivar, under continuous stocking with sheep. Turves (250 × 250 mm), from which individual plants were carefully extracted, were taken every month during 1990–91 (years 2 and 3 after sowing). Each plant was described in detail by assessing a range of morphological characters. Information was also gathered from each quadrat on the degree of flowering and seedling recruitment. There were clear seasonal variations in plant size and complexity with an increase in the number of simple, unbranched plants over the winter/spring period, which became the dominant plant type by June. During the later part of each year, the reverse was true. Characters associated with plant size also decreased over the winter period, followed by recovery during the ensuing summer. However the recovery was not complete and there was a strong general trend towards an increased proportion of less complex plants of reduced size over the 2 years. As plant size fell, plant number increased and morphological differences between cultivars diminished. By autumn of the second year (third year after sowing) the mean plant size reached a critical level with further stolon loss resulting in large scale plant death. Over the 2-month period August–October 1991, plant number fell by 60% and resulted in a reduction in stolon abundance of 76%; a true clover crash. The seedling data also suggest that under these conditions seedling recruitment can be up to one twentieth of that expected from a conventional sowing and can play a substantial role in the regeneration of the sward.

In 1989 and 1990, small, medium and large seed tubers, cv. Désirée, were planted 38 cm apart in experiments designed to measure the effects of different combinations of neighbouring plants on the yield and size of tubers from individual plants. Total yield, ware yield (> 150 g), numbers of tubers and numbers of stems increased as seed tuber size increased. Also, decreasing the size of seed tubers decreased the numbers of tubers in all sizes except those > 200 g. Competition from the two neighbouring plants on either side in the same row (first neighbours) increased as the size of seed tubers increased and with all seed sizes yields decreased. For example, plants from large seed benefited from small seed planted as neighbours whereas, with plants from small seed, yield was decreased with neighbouring plants from large seed. Numbers of stems and tubers were not affected by neighbouring plants. Also yields were not affected by the two plants adjacent to the first neighbours (second neighbours) or by the size of seed tubers planted in adjacent rows. Competition from first neighbours also affected tuber size distributions and, with small seed, increasing the competition decreased the number of tubers > 150 g and increased numbers < 50 g. Medium and small seed planted as neighbours of large seed increased numbers of tubers > 150 g. When yields from plants produced by seed of each size with similarly sized seed planted as first neighbours (uniform populations) were compared with mixed populations, yields were always greater from the mixed populations of different seed sizes planted alternately than from the means of uniform populations. Therefore in the mixed populations, there were larger gains from the larger seed than losses from the smaller seed.

Many biological experiments and almost all quantitative genetic studies draw conclusions from differences between families. Such differences are caused as much by heritable as by non-heritable sources. This paper investigates the impact of seed quality on the expression of quantitative variability among 20 highly inbred lines of Nicotiana rustica using ten seed categories representing different pollination times, seed sizes, seed positions in the capsule and seed maturity. Analysis of variance revealed that while the mean performance of the inbred lines remained more or less the same across all the seed categories, their individual performances differed widely, showing a highly significant interaction between lines and seed categories. This interaction accounted for up to 12% of the total variation and was largely attributable to late pollinations and immature seed. Seed categories were also the main source of heterogeneity among the within-line variances, but only immature seed lowered the correlation between the inbred means. In general, seed quality affected the developmental characters much less than the traits measured at or after flowering, and the expression of genetic variation was not critically affected by seed size or position. Immature seed, on the other hand, generated the highest level of unreliability in the comparative performance of lines and such seeds should therefore not be used in quantitative genetic experiments under any circumstances. Further implications of seed quality effects on the interpretation of genetic components are discussed in detail.

The effects of short-term waterlogging during the vegetative, reproductive and total growth phases were investigated in four cultivars of cowpea (Vigna unguiculata L. Walp) in relation to their controls in a pot experiment conducted at the University of the West Indies, St. Augustine, in 1989. All cultivars were able to recover completely and produce near to normal yields, when waterlogging was confined to the vegetative period. Recovery growth was affected in cultivars waterlogged during the total growth phase and the plants were significantly smaller (P < 0·05) in vegetative dry matter (60–80% of the size of their respective controls) even at maturity. Recovery growth was affected, to a greater extent, in cultivars possessing a small mainstem[ratio ]branch ratio. Yield development in the waterlogged plants was affected by accelerated leaf senescence and consequent reduction in the reproductive period. As a result, yields in all the cultivars tested were significantly smaller (P < 0·05) than their respective controls and varied between 54 and 60% of the controls. Plants waterlogged during the reproductive phase were not significantly different (P < 0·05) in vegetative dry matter from the controls, but showed root degeneration and accelerated leaf senescence in all but one cultivar (Local Red). Yield reduction, however, was significant (P < 0·05) only in IT-83S-898. Possible criteria for selecting plants tolerant to waterlogging are discussed.

Five British hill sheep breeds and their crosses were compared on a hill farm in a common environmental and husbandry system in 1974 in Peeblesshire, Scotland. A home-bred Scottish Blackface stock was maintained, and ewes were crossed with rams of each of the five hill breeds, North Country Cheviot, Derbyshire Gritstone, Exmoor Horn, Swaledale and Scottish Blackface. The crossbred female progeny were then mated half to homebred Blackface rams and half to rams of the paternal breed. This was reversed in later generations to form a continuous criss-crossing system. The performances of the crossbred ewes and of the crossbred lambs were compared, and the effects of the breeds and the average heterosis were estimated. A total of 5579 ewe and 6516 lamb records were available for comparison over an 8-year period from 1977 to 1984. Some 20 rams per breed were used over this period. The Swaledale crosses had substantially higher output and efficiency than any of the other crosses, while the Derbyshire Gritstone and Exmoor Horn crosses were generally inferior. There was appreciable heterosis for most traits, that for fleece weight and for litter weight at weaning being the highest. The heterosis for output per ewe exposed and efficiency of lamb production are positive and significant. The results support greater use of the Swaledale and of a crossbreeding system with Blackface to exploit heterosis in harsh hill farm conditions.

Two experiments were carried out at Mt. Cotton, The University of Queensland, from November 1992 to July 1993, to study the effect of extent of digestion or feed type (grass or legume) on particle kinetics in the rumen. Small (0·5–1·18 mm) Yb-labelled grass or legume particles, either digested or undigested, were injected into the rumen of sheep fed on different diets, and their retention time in the reticulo-ruminal compartment measured. In Expt 1, four intact wethers were fed on either pangola grass hay, chaffed lucerne hay, pelleted lucerne hay or commercial pelleted concentrate. Digested particles from the faeces of animals fed on pangola or lucerne and undigested material from the same diets were wet-sieved and the fraction 0·5–1·18 mm collected, labelled with Yb-acetate and injected into the animals together with a solution of Cr-EDTA. Faecal samples were taken and analysed for marker concentrations. In Expt 2, four similar animals, fitted with duodenal and ruminal cannulae, were fed on different proportions of pangola grass hay and lucerne hay, and Cr-EDTA and the above mentioned labelled particles were injected through the rumen cannula. Samples were taken from the duodenum and analysed for marker concentrations.

The results indicated that diet characteristics rather than extent of digestion or particle type had the greatest influence on rates of passage of both liquid and particulate phases. Different proportions of pangola and lucerne did not result in marked differences in either the volumes of rumen contents or the rates of passage of the solid phase marker but altered the rates of passage of Cr-EDTA. Increasing the proportion of legume increased intake and decreased retention time markedly, with no additive effects on digestibility.

Particles of the same small size escaped with the same fractional passage rate within each diet, irrespective of type (grass or legume) or status (undigested or digested), indicating identical kinetics within each rumen type.

It was concluded that rumen conditions as influenced by diet type have most influence on water and particle kinetics and that extent of digestion of the small particles used in our experiments was not important. Particles of legume or grass of the same size behaved similarly within a diet type.

The objective of this study was to develop an experimental model to measure both fractional and absolute rates of protein synthesis in the small intestine of lambs. Six male castrate lambs (∼6 months old, mean liveweight 26 kg) were offered, via continuous feeders, 900 g/day lucerne chaff. They were prepared with catheters in the cranial mesenteric vein (CMV), femoral artery (FA), jugular vein and abomasum, and a blood flow probe around the CMV. Cr-EDTA (0·139 mg Cr/ml, ∼0·2 ml/min) was infused abomasally for 24 h and L-[2,6-3H]phenylalanine (Phe) (441±33·8 μCi into the abomasum) and L-[U-14C]phenylalanine (43·9±4·08 μCi into the jugular) were also infused during the last 8 h. Blood from the CMV and FA was sampled during isotope infusions. At the end of infusions, lambs were killed and tissue and digesta samples removed from four sites along the small intestine (SI). Transfers of labelled and unlabelled Phe were measured between SI tissue, its lumen and blood, enabling both fractional and absolute rates of protein synthesis and gain to be estimated. The total SI protein pool was 84 (±1·7) g and fractional gain rate was 7·5 (±5·5)% per day. Mean protein synthesis and fractional synthesis rates (FSR) were calculated from the mean retention of 14C and 3H in SI tissue. FSR tended to increase caudally along the SI (although P > 0·05). The choice of free Phe pool for estimating precursor specific radioactivity (SRA) for protein synthesis had a significant effect on FSR. Assuming that tissue free Phe SRA represented precursor SRA gave a mean FSR of 129 (±24)% per day. Corresponding estimates for free Phe SRA in the FA and CMV were 20 (±1·8) and 30 (±3·1)% per day respectively. The correct value for protein synthesis was therefore in doubt, although indirect evidence suggested that blood SRA (either FA or CMV) may be closest to true precursor SRA. This evidence included (i) comparison with flooding dose estimates of FSR, (ii) comparison of 3H[ratio ]14C Phe SRA in free Phe pools with this ratio in SI protein, and (iii) the proportion of SI energy use associated with protein synthesis. Advantages of the present experimental model compared to other methods included (i) measurements of both protein synthesis and gain, and hence, all components of turnover, (ii) measurement of absolute as well as fractional rates of synthesis and gain, (iii) inclusion of proteins which are synthesised and exported, and (iv) concurrent measurement of protein synthesis and energy utilization by the small intestine.

This study used an experimental model, described in a companion paper, to examine the effects of feed intake on protein turnover in the small intestine of lambs. Ten male castrate lambs (∼ 10 months old) were offered, via continuous feeders, either 400 (n = 5) or 1200 (n = 5) g/day lucerne chaff, and mean experimental liveweights were 28 and 33 kg respectively. All lambs were prepared with catheters in the cranial mesenteric vein (CMV), femoral artery (FA), jugular vein and abomasum, and a blood flow probe around the CMV. Cr-EDTA (0·139 mg Cr/ml, ∼ 0·2 ml/min) was infused abomasally for 24 h and L-[2,6-3H]phenylalanine (Phe) (420±9·35 μCi into the abomasum) and L-[U-14C]phenylalanine (49·6±3·59 μCi into the jugular vein) were also infused during the last 8 h. Blood from the CMV and FA was sampled during the isotope infusions. At the end of infusions, lambs were killed and tissue (n = 4) and digesta (n = 2) samples removed from the small intestine (SI) of each animal. Transfers of labelled and unlabelled Phe were measured between SI tissue, its lumen and blood, enabling both fractional and absolute rates of protein synthesis and gain to be estimated.

Total SI mass increased significantly with feed intake (P < 0·05), although not on a liveweight basis. Fractional rates of protein gain in the SI tended to increase (P = 0·12) with feed intake; these rates were −16·2 (±13·7) and 23·3 (±15·2) % per day in lambs offered 400 and 1200 g/day respectively. Mean protein synthesis and fractional synthesis rates (FSR), calculated from the mean retention of 14C and 3H in SI tissue, were both positively affected by feed intake (0·01 < P < 0·05). The choice of free Phe pool for estimating precursor specific radioactivity (SRA) for protein synthesis had a major effect on FSR. Assuming that tissue free Phe SRA represented precursor SRA, mean FSR were 81 (±15) and 145 (±24) % per day in lambs offered 400 and 1200 g/day respectively. Corresponding estimates for free Phe SRA in the FA and CMV were 28 (±2·9) and 42 (±3·5) % per day on 400 g/day, and 61 (±2·9) and 94 (±6·0) on 1200 g/day. The correct value for protein synthesis was therefore in doubt, although indirect evidence suggested that blood SRA (either FA or CMV) may be closest to true precursor SRA. This evidence included (i) comparison with flooding dose estimates of FSR, (ii) comparison of 3H[ratio ]14C Phe SRA in free Phe pools with this ratio in SI protein, and (iii) the proportion of SI energy use associated with protein synthesis.

Using the experimental model, the proportion of small intestinal protein synthesis exported was estimated as 0·13–0·27 (depending on the choice of precursor) and was unaffected by feed intake. The contribution of the small intestine to whole body protein synthesis tended to be higher in lambs offered 1200 g/day (0·21) than in those offered 400 g/day (0·13). The data obtained in this study suggested a role for the small intestine in modulating amino acid supply with changes in feed intake. At high intake (1200 g/day), the small intestine increases in mass and CMV uptake of amino acids is less than absorption from the lumen, while at low intake (400 g/day), this organ loses mass and CMV uptake of amino acids exceeds that absorbed. The implications of these findings are discussed.